GB2167694A

GB2167694A - A device for monitoring the shape of metal shavings, during the machining of metal

Info

Publication number: GB2167694A
Application number: GB08526895A
Authority: GB
Inventors: Manfred Reissig
Original assignee: Werkzeugmaschinenkombinat 7 Oktober VEB
Current assignee: Werkzeugmaschinenkombinat 7 Oktober VEB
Priority date: 1984-11-01
Filing date: 1985-10-31
Publication date: 1986-06-04
Also published as: JPS61110035A; GB2167694B; DD227919A1; FR2572321A1; GB8526895D0; DE3533525A1

Abstract

In a device for use in automatic turning machines the shavings act as electrical contact members to complete a circuit to a processing circuit via the tool (2) held in the tool clamping device (1) and a point of contact in the shaving space. The tool clamping device (1) is provided in the immediate vicinity of the clamping location of the tool (2) on the front face facing the workpiece and the immediately adjacent lateral surfaces with an electrically conductive coating (4) insulated with respect to the base of the tool clamping device, which coating is connected to a transmission line (12) passing through the interior of the tool clamping device (1), and led outwardly via a point of connection to a processing circuit by means of which a signal output "coiled shaving" is activated during permanent contact and a signal output "long shaving" is activated during intermittent contact. <IMAGE>

Description

SPECIFICATION A device for monitoring the shape of metal shavings, chips or turnings produced during the machining of metal A device for monitoring the shape of shavings during the milling of metal with respect to long unbroken shavings and shavings wound around the tool, which shavings act as contact elements by the use of their electrical conductivity and form a processing circuit by means of the tool held in a tool clamping device and a point of contact in the shaving space, in particular for automatic turning machines.

During turning, the monitoring and control of the shavings is a major problem as regards the development of production units requiring few operators.

Undesirable shaving shapes such as tangled ones or ribbon shaped ones frequently lead to damage to the surface of the workpiece and hinder the automatic exchange of tools and workpieces. In addition, the risk of tool breakage is increased.

Tangled and ribbon shaped shavings also hinder transportation of the shavings as they require a considerable space requirement for their transportation. All these disadvantageous side effects of undesirable shaving shapes lead to machine stoppages and the risk of accidents during removal of the shavings.

Widely differing methods of preventing the formation of these tangled or ribbon shaped shavings have already been used. For example the breakage of the shaving is caused by the corresponding formation of the tool cutting edges or by additional pivot movements superimposed on the feed drive.

A further possibility is provided by technological advances in cutting parameters aimed at short shavings.

In the case of automatic machine tools which are equipped with a plurality of different tools (tool stores and automatic tool exchange) and are programmed with optimum cutting values for economic reasons, it is not possible to prevent the formation of undesirable shaving shapes with any reliability. This is due to the large number and the widely differing properties of the machine tool/tool/ workpiece system having an effect on the shape of the shavings. It is not possible at present to predetermine the shape of the shavings with sufficient reliability.

Consequently the methods being developed at present to prevent damage arising from undesira ble shaving shapes involve the use of devices which automatically detect the shape of the shav ings.

Known devices for detecting the shape of shav ings are based on a measurement of the heat radiation or the ultrasonic reflection of the shavings removed. A further known device for monitoring the shape of shavings uses approximation initiators and light barriers. The dynamic feed force component has also been used to detect the shape of the shavings.

It has also been attempted to detect the shape of shavings by detecting the shaving removal direction. For this purpose, a respective contact member is disposed in an insulated manner at three different points of the cutting and free surface of the turning tool, via which members a circuit is closed to a processing circuit by means of the shaving being removed.

None of these known solutions have been found to be effective in practice up to now. They are all laboratory prototypes with sensors designed for this purpose which are not suitable for use in normal production conditions as they crowd the operating space of the machine and hinder the automatic exchange of tools and workpieces. The operation of most of these sensors is impaired by the use of auxiliary production materials. In addition, the costs of obtaining and transmitting the electrical signals are very high. In the case of machine tools with automatic tool exchange with contact sensors disposed on the tools, additional signal transmission problems are involved in ensuring reliable operation with a suitable degree of technical complexity.In addition, the sensors have a varying level of sensitivity as regards external force effects and are subject to damage by the removal of shavings.

According to the invention there is provided a device, more particularly for automatic turning machines, for monitoring the shape of shavings during the machining of metal with respect to long unbroken shavings and shavings coiled around the tool, said shavings acting as contact members by the use of their electrical conductivity to complete a circuit to a processing circuit via the tool held in the tool clamping device and a point of contact in the shaving space, the tool clamping device being provided with an electrically conductive coating insulated with respect to the base of the tool clamping device, in the immediate vicinity of the clamping location of the tool on the front face thereof facing the workpiece and on the immediately adjacent lateral surfaces which coating is connected to a transmission line passing through the interior of the tool clamping device, which line is led outwardly via a point of connection to the processing circuit by means of which a signal output "coiled shaving" is activated during permanent contact and a signal output "long shaving" is activated during intermittent contact.

The preferred embodiment of the invention provides a device for monitoring the shape of shavings during the machining of metal with respect to long unbroken shavings likely to wind themselves around the tool, which device operates reliably irrespective of roughing or finishing machining as well as during the use of auxiliary production materials, in which the contact members are spaced from the tool and are not detrimental to the operation of the machine or the exchange of workpieces and tools.

Furthermore, in the preferred embodiment, the tool clamping device is provided in the immediate vicinity of the clamping location of the tool on the front face facing the workpiece as well as the im mediately adjacent lateral surfaces with an electrically conductive coating isolated with respect to the base of the tool clamping device. This coating is electrically connected through the interior of the tool clamping device by a wire which is led externally via a point of connection to the processing circuit, by means of which, during permanent contact, a signal output "coiled shaving" is activated and, during intermittent contact a signal output "long shaving" is activated.

Wear-resistant sheets of material are preferably disposed in an insulated manner on the surfaces of the tool clamping device and act as the electrically conductive coating. These sheets of material are advantageously made of non-magnetisable material.

In the case of a tool clamping device which is part of a turret head, the point of connection is formed as an inductive approximation initiator.

In the case of a wireless measurement signal transmitter which is already provided and which is designed to take the measurement signals from an exchangeable measurement sensor in the turret head and transmit the measurement signals from the turret head to the fixed workpiece support component, the reception location of the measurement signal transmitter disposed on the fixed workpiece support component is connected via a gate circuit with the processing circuit.

The signal output "coiled shaving" is preferably activated in the case of a predetermined permanent contact time in the range of 0.5 to 4 seconds and the signal output "long shaving" is preferably activated in the case of a predetermined contact frequency in the range of 2 to 50 l Iz. The signal output of the processing circuit is connected to a nominal value source increasing the feed drive in a stepwise manner.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of a tool clamping device for a turning machine, Figure 2 is a top view of the tool clamping device of Figure 1, Figure 3 is a section taken along the line A-B of Figure 1, Figure 4 shows a circuit arrangement for generating an electronic signal for use with the device of Figures 1-3, Figure 5a shows the signal curve for broken shavings.

Figure 5b shows the signal output curves for an unbroken shavings, a coiled shaving and a long shaving deduced therefrom by a processing circuit (not shown).

A device for monitoring the shape of shavings will be described with reference to the standard turning tool clamp 1 shown in Figures 1 & 2. A turning tool 2 equipped with a cutting element 2a is held in turning tool clamp 1 which has a cylindrical take-up la by means of which it is fastened in a disc turret 3 (see Figure 3). An electrical contact member 4 is fastened to the tool clamp 1, and surrounds the surfaces thereof close to the outlet of the turning tool 2, i.e. has its surface shape adapted thereto. The contact member 4 is of nonmagnetisable sheet steel. Suitable insulating substrates 5 are provided to insulate the contact member 4 from the tool clamp 1. The contact member 4 is screwed to the tool clamp 1 together with the insulating substrate 5 by means of insulating bores 6,7.8 for screws 9, 10 provided in the tool clamp 1.

The contact member 4 is connected at a fastening location, via the screw 10 provided with a cylindrical insulating sleeve 11 in the turning tool clamp 1, to which sleeve there is connected a wire 12 which passes through the interior of the tool clamp 1 and is connected to an induction coil 13 (see Figure 3).

The other input of the induction coil 13 is connected by wire 14 to earth, i.e. to the tool clamp 1 and therefore the tool cutting element 2a. The induction coil 13 is held in a housing 15 which is provided in a cylindrical recess in the front face of the cylindrical take-up la of the tool clamp 1. and fastened thereto by screw 19. The induction coil 13 is disposed directly opposite an approximation initiator 16. A housing 17 receiving the approximation initiator 16 is fastened to fixed workpiece support component 18. The air gap between the induction coil 13 and the approximation initiator 16 may be adjusted by a spacer disc 20.

The circuit diagram of Figure 4 shows the induction coil 13 which may be short-circuited between the contact member 4 and the tool cutting element 2a by means of a metal shaving shown as a switching contact 21. A torquf induction coil 22 belonging to the approximation initiator 16 is disposed in an oscillator circuit which is shown by a capacitor 23 connected to the torque induction coil 22. The signals supplied via wire 24 in Figure 3 are supplied to a processing circuit (not shown).

The metal shaving being removed produces, when it contacts the contact member 4, the signals which are shown in graph form in Figure 5 over a time period t. Figure 5a shows a non-uniform signal curve in which contacts of different length give rise to both short pulse-like signals and longer signals. Figure 5b shows three characteristic signal curves.In a first time period TLs only one signal is produced which disappears again within the predetermined contact period Twos. In a second time period TLs an accumulation of pulse signals is produced, reaching a pulse limit number of nine pulses which result from the predetermined contact frequency and the time period T,,. In a further time period TLs a permanent contact is made by the shaving being removed which exceeds the predetermined permanent contact time Twos. The signal "coiled shaving" or the signal "long shaving" are activated by the processing circuit as a result of the fact that the pulse limit number igrenz or the predetermined permanent contact time TWs have been exceeded.

The operation of the device for monitoring the shape of shavings is as follows: The shaving being removed by machining with the tool cutting element 2a and acting as the switching element 21 produces a signal level H during contact with the contact member 4. If the circuit from the shaving to the contact member 4 is not closed, the signal level remains at its initial value L.

Consequently, in the case of all short broken shavings no H-signal is produced at all. Only longer shavings which contact the contact member 4 lead to the signal level H. If these shavings break shortly thereafter by themselves, i.e. before the predetermined permanent contact time Tws is reached, no action on the machining process is required. The contact of the shaving being removed is only detected by the processing circuit as the permanent contact time Tws and the signal "coiled shaving" WS transmitted when this time limit is exceeded. In this case, the shaving being removed has generally wound itself around and jammed the turning tool.If the shaving being removed only closes the circuit for short repeated periods, leading to the formation of the pulse signals, the risk of a dangerous long shaving may be exluded as long as the pulse limit number igrenz is not reached during the time period T,sl i.e. in this embodiment as long as nine pulses per time period TLs is not exceeded. The signal "long shaving" LS is only transmitted by the processing circuit if the count exceeds the pulse limit number i The occurrence of these pulse frequencies is therefore evaluated with respect to the shaving formation as a dangerous long shaving, as long shavings producing multiple contact frequently lead to the formation of coiled shavings in the case of very slight changes in cutting conditions.In many cases it is therefore possible, by detecting dangerous long shavings and subsequent changes in machining parameters, to prevent the occurrence of coiled shavings which need to be avoided at all costs.

Each contact of the shaving with the contact member 4 leads to the damping of the oscillator circuit of the approximation initiator 16 as a result of which the above-mentioned H-signal is produced and supplied to the processing circuit. If this damping is countered by opening of the switching contact 21, the signal is reset to L. A possible strategy would be, for example, to increase the feed of the machining process with a specific step increment to a predetermined limit value on transmission of the "long shaving" LS and/or "coiled shaving"WS signals in order to achieve an im proved shaving shape or shaving breakage. Use may be made, for this purpose, of a nominal value source which increases in a stepwise manner in the case of a call signal. If the signal "coiled shav ing" WS continues despite this procedure, it is then necessary to signal that action to remove the shavings wound around the tool is necessary. Sig nalling for manual action on the machining proc ess may also be provided if the "long shaving" signal LS continues.

Claims

1. A device, more particularly for automatic turning machines, for monitoring the shape of shavings during the machining of metal with respect to long unbroken shavings and shavings coiled around the tool, said shavings acting as contact members by the use of their electrical conductivity to complete a circuit to a processing circuit via the tool held in the tool clamping device and a point of contact in the shaving space, the tool clamping device being provided with an elec tricaily conductive coating insulated with respect to the base of the tool clamping device in the immediate vicinity of the clamping location of the tool on the front face thereof facing the workpiece and on the immediately adjacent lateral surfaces, which coating is connected to a transmission line passing through the interior of the tool clamping device, which line is led outwardly via a point of connection to the processing circuit by means of which a signal output "coiled shaving" is activated during permanent contact and a signal output "long shaving" is activated during intermittent contact.

2. A device as claimed in claim 1, wherein wear-resistant metal sheets are disposed in an insulated manner on the tool clamping device to act as the electrically conductive coating.

3. A device as claimed in claim 2 wherein the wear-resistant sheets are of non-magnetisable material.

4. A device as claimed in any of claims 1 to 3, wherein the point of connection is formed as an approximation initiator when the tool clamping device is formed as part of a turret head.

5. A device as claimed in any of claims 1 to 4 wherein the reception location of the measurement transmitter is connected via a gate circuit with the processor circuit when a measurement signal transmitter is disposed between the turret head and the fixed tool support component for the purposes of taking up the measurement signals from an electrical measurement sensor provided in the turret head.

6. A device as claimed in any of claims 1 to 5, wherein the signal output "coiled shaving" is activated in the case of a predetermined permanent contact period (tows) lying in the range of 0.5 to 4 seconds.

7. A device as claimed in any of claims 1 to 6, wherein the signal output "long shaving" is activated in the case of a predetermined contact frequency lying in the range of 2 to 50 Hz.

8. A device as claimed in any of claims 1 to 7, the signal output of the processing circuit is connected to a nominal value source increasing the feed drive in a stepwise manner.

9. A device for monitoring the shape of shavings during the machining of metal substantially, as herein described with reference to the accompanying drawings.

10. A device for monitoring the shape of shavings during the machining of metal, said shavings, in use, acting as electrical contact members to complete a circuit to a processing circuit via the tool held in the tool clamping device and a point of contact in the shaving space, the tool clamping device being provided with an electrically conductive coating insulated with respect to the base of the tool clamping device in the immediate vicinity of the clamping location of the tool which coating is electrically connected to the processing circuit whereby a signal output "coiled shaving" is activated during permanent contact in the shaving space and a signal output "long shaving" is activated during intermittent contact in the shaving space.